Rail heat treatment



Patented Dec. 22, 1931 UNITED STTES PATENT OFFICE EDWABD I. IENNEY, 01'PMSYLVANA, ASSIGNOE '1'0 :mam

' STEEL COMPANY, .A. OOBPOBATION 01' PENNSYLVANIA.

nan. mur 'rammm Application filed April 29, 1931. Serial Io. 583391.

My invention relates to the heat treatment of rails and other massivebodies. This a plication is a continuation in part of app cation SerialNo. 377 ,7 filed July 12, 1929.

An important object of my invention is the 5 revention of permanentstrains in the metal of rail or other massive body which tend to beproduced therein during cooling, particularly during such rapid coolingas occurs during quenching.

When a rail is sub'ected toa rapid cooling operation, marke temperaturedifl'erentials are produced between different portions of the railmetal. These diflerentials of temperature, particularly those betweenthe interior and exterior portions of the head, produce more or lesssevere strains in the metal, which may result in permanent weaknesses orother defects in the rail, if the rail is allowed to cool in the usualway. It is an important purpose of my invention to prevent these strains'from resulting in permanent defects in the metal. Accordingly, asignificant feature of my invention is the elimination of these strainswhile the rail is still hot. This I accomplish by subjecting the rail,while in its condition of having marked temperature difl'erentials, to arapid heating operation to quickly reduce the temperature 30diflerentials.

To illustrate my invention a specific embodiment thereof will now bedescribed. The drawing gives a cross section, full sized, of a rail towhich this specific description applies.

35 This rail weighs about 130 lbs. per yard, is

Manga- Phoe- Carbon ne Dhoma Sulphur Silicon A rail'of the cross sectionshown is produced in the rail mill in the usual way. The rail is allowedto cool from the mill heat un- 0 til an 'edge of one of the flangesbecomes magnetic. Obviously, at this stage, by 'far the greater mass ofthe rail is still above the critical range. In this state the rail isimmersed in a water bath for 30 seconds and is then removed andimmediately transerred u to and immersed in a bath of molten lead havinga temperature of about 1000 F. It is kept in this lead bath a eriod offrom 4 to 5 minutes. From the lea bath it'is immediately transfer-'redto a closed furnace which go althou h it may be kept in this furnace ana somew at greater len h of time, sa up to three hours. The ral is thenwit drawn from the furnace and allowed to cool in the air.

The treatment of the rail just outlined qo comprises first, rapidlycooling the greater part of the rail metal through the critical range;second, the ra id reduction of temperature difierentials n the rail inthe lead bath, which difl'erentials have been produced 15 by the rapidcooling operation; third, drawing the metal of the rail in the furnace,that is to say, producing a sorbitic or troostite-sorbiticmicro-structure in the hardened metal;

and fourth, cooling the rail to atmospheric 00 temperatures.

The rapid cooling of the rail metal occurs not only while the rail isactually in the aqueous quenching bath but continues through theinterval which elapses between 85 the removal from the water bath andthe immersion in the lead bath; While the immersion in the lead bath"immediately follows the removal from the water bath `it will be obviousthat in handling an ob ect such as a rail the time interval between thetwo steps must necessarily be of appreciable duration. In treating fullsized rails of the section shown I have ordinarily kept this timeinterval at twenty seconds or less. It is well to bear in mind, however,that the rapid cooling operation continues for a short interval afterthe removal from the actual quenching bath.

'This step of rapidly cooling the rail producea very marked difierencesof temperature in diflerent parts of the raiL The thinner as the webandflanges, will be at subtantally lower temper'atures than the head;

- the exterior portions of the rail will be at When the rail is immersedin the lead bath I a goodl proportion of the rail mass is still above eblue heat zone. Particularly is this true of the head. While the rapidcooling operation has been suflicient to lower the temperature of theentire mass of rail metal to temperatures below the critical range, theinterior of the head is still above the blue heat zone. This isimportant as the elimination or substantial reduction of temperaturedifferentials in the head while a considerable mass thereof is stillabove the blue heat zone tly diminishes the chances of permanent efectsfrom the strains produced by temrature diflerentials. Four to fiveminutes n the lead bath for thisparticular section of rail, cooled asabove, is suflicient to subtatially equalize the temperatures of the Asabove indicated, the rail is next taken from the lead bath to a furnacemaintained at about 1000 F. for drawing the metal of the rail which haspassed rapidly through the critical range, with the resultingtransformation of the micro-structure of this metal to the sorbitic ortroostite-sorbitic state. Following this the rail is allowed to cool inthe air.

A modification of the process just outlined has n very successful.Following a quench in water for seconds, as in the previous example, therail is immersed in a lead bath having a temperature of 850 to 875 F.for three minutes, and then immediately 'transferred to the drawingfurnace having a temperature of 850 to 875 F. in which it is held for 1hours. By using lower temperatures than in the previous examplesubstantially higher mechanical properties such as tensile strength andelastic limit are secured.

In these two illustrations of the invention the temperatures employedfor the lead bath and the durations of immersion therein aresuflicientto efl'ect substantial equalization of the temperatures of therail. While sub- 66 etantial equalization is desired, successful resultsmay also be obtained where complete uniformty of temperatureis notsecured.

For example, following the uench, 'the rail precia le diflerences oftemperature between ortions of the rail but they will be so reuced thatequalization of temperature will be quickly accomplished when the railis placed in the drawing furnace. The imary function of the lead bath isto %uiuy reduce the temperature diflerences in t e whether suchreduction of temperature differences is carried to a condition oftemperature uniformity or not.

The process ust described may be modified by efiecting the drawingoperation in the lead bath instead of in the furnace. Instead of keepingthe rail in a lead bath just long enough to reduce temperaturedfierentials, as in the process just described, the immersion in thelead bath is prolonged sufliciently to eflect the drawing operation.Instead of an immersion in the lead bath for a period of from four tofive minutes, the immersion will be maintained for one hour or longer.After withdrawal from the lead bath the rail is allowed to cool in theair.

Obviously the time periods given for rapid cooling, lead bath treatment,and drawing will va somew-hat with the particular section an weights ofmetal treated. The figures given have been found to be effective withthe particular section shown.

The best results have been obtained when the entire mass of the railhead has been rapidly cooled through the critical range but obviously mprocess is not limited to such treatment. or example, the rapid coolingoperation may be so limited in duration that `a substantial portion ofthe 'interier of the rail head is not rapidly cooled through thecritical range, and only a portion of the head metal therefore beinghardened.

Obviously the process may be altered in various wa s. For example,instead of cooling from the mill heat until an edge of the flangebecomes magnetic and then quenching, as above given, the rail may beequalized at a definite temperature above the critical range and thenquenched.

Although it is advantageous to quench from the mill heat, whether or notan equalizing operation is employed prior to the quench, it may bedesirable at times to reheat and treat rails which have already beencooled to atmospheric temperaturesl Obviously in such case the rail maybe heated above the critical range and then treated in accordance withthe methods already outlined.

In several of the claims which follow reference is made to the head onlyof the rail, the other parts of the rail not being mentioned. Obviouslsuch claims arenot in-' tendedto be limited to methods in which the headalone is treated. These specify the head because of the fact that thisportion of the railis the most important as regardsmy ,treat-ment andthe process is eficetive 'whether or not the other s of the rail aretreated. Obviousl it s correct to refer to the 'head having' subjectedto the steps of my process whether or not the remaimng of the rail .havebeen also subjected ereto. Instead of a lead bath for quickly reducingtemperature diflerences other li uid baths ma be successfully employed.or example have found certain salt baths to be successful. As auillustration mention may be made of a salt bath made of equalbefore itis placed in t e drawing furnace and when the temperature of the saltbath is 875 F. about five to six minutes is sufficient.

As is evident from the illustrative embodiments of the invention givenabove the temperatures of the li uid bath may vary considerably. Preferal the tem eratures of such bath should not e below t e blue heat zone.

What 'I desire to emphasize in this connection is that the importantthing is to rapidly transfer heat to the rail to quickly reducetemperature difierences and ths may be eifected in a metal bath, 'aslead', or in some other'fluid material as for example various saltmixtures. i v

What I mean by the blue-heat zone, as this expression is used in thisdisclosure, is that range of temperatures, below the critical rangewhere steels in heatin increase in tensile strength and the elasticlimit, and also decrease in ductility. At temperatures, within thisrange, most steels when exposed to air take on a blue color, due tooxidation,

but since, with some steels, this color is not' readily apparent, I donot wish to be limited to the color as a means of determining or definngthis zone. V

By the expression critical range I mean that temperature range throughwhich the steel must be cooled to eflect a. hardening thereof.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent is:

. 1. In'a process for the treatment of rails, the steps of rapidlycooling arail to cause a substantial portion of at least the head of the-rail to pass rapidly through the critical and then immer-sing the railwhile still hot in a liquid bath maintained at a temperature not lowerthan the blue heat zone tials n e rail.

2. In a process for the heat treatment of f rails, the steps ofimmersing a rail, the major 'and then before the innermost portions ofthe head have reached the blue heat zone iners-'` ing the rail in aliquid bath maintained at a temperature not lower than the blue heatzorie to quickly reduce temperature differentia s.

3. In a process for the treatment of rails, the step: of rapidly coolinga rail and then, while t e innermost portions of the head of the railare still above the blueheat zone, subjectin the rail to-'a hot liquidmetal'of high speci c gravity to quickly reducethe temperaturediflerentials.

4. In a process for the treatment of rails, the steps of rapidly coolingthe rail, a substantial proportion of at least the head of the railbeing passed rapidly through the critical range, immersing the railwhile still hot in a liquid bath maintained at a temperature not lowerthan the blue heat zone to rapidly reduce the temperature difl'erentialsin the rail and then subjecting the rails to a drawing operation in afurnace.

5. In a process for the treatment of rails, the steps of rapidly coolinga'rail whereby marked temperature diflerentials are produced and thenimmersing the rail while still hot in a liquid bath maintained at atemperature not lower than the blue heat zone to quickly reduce thetemperature diflerentials.

6. In a process for the treatment of ferrous metal bodies, the steps ofrapidly cooling the object whereby marked temperature diflerentials areproduced between portions of the body and then immersing the objectwhile sti-ll hot in a liquid bath having a temperature not lower thanthe blue heat zone to quickly reduce the temperature diiferentials.

7. In a process for the treatment of ferrous metal bodies, the steps ofrapidly cool-a ing the bodies in an aqueous medium whereby 'a markedtemperature differential is proat least a portion of the body throughthe to rapidl reduce the temperature difierencritical range and therebyroducing marked temperature difl'erentals %etween difierent portions ofthe body, and then immersing while the .body while still hot in a saltbath having a temperature notlower than the'bhe heat zone to quicklyreduoe *the temperature differentials.

9. In a process for the treatment of rails. the* ste 'of rspidly coolinga rail and then, e innermost portions of the head of the rail are stillabove the blue hoat zone, immersing the' rail in a, molten bath of leadto quickly reduce the temperature dfierenti'als.

In testimony whereof I hereunto aflix my signature.

EDWARD F. KENNEY.

